The present invention relates to the field of servo shields used in small Winchester disk drives to minimize undesired crosstalk between a data read/write head used in a "stack" of hard disks and servo information that is recorded on an adjacent disk.
In the past, to insure good tracking performance, one surface of a disk in a stack of hard disks rotated by a spindle is provided with "servo" information which, as is conventional, is used to make certain that the head drive assembly, or actuator, positions the heads above the center of a data track regardless of thermal effects or other factors that might introduce errors. The use of a "servo surface" on one of the disks in a disk drive is well known.
It is also known that a head which writes data onto or reads data from a surface (that is, a head other than the servo head) might generate "fringing" electromagnetic fields that can be picked up by the servo head (that is, the head that normally reads the servo information on the servo surface) to introduce errors into the servo loop. Crosstalk between the wires connected to the read/write head and servo head have also been encountered. To avoid such crosstalk, the servo surface in small Winchester disk drives is almost always provided on the bottom surface of the lower-most disk. This placement has resulted since the disk itself shields leakage and fringing fields from reaching the bottom surface of the lower-most disk. In order to prevent crosstalk interference from the data head fringing field to the servo head, magnetic shields have been affixed directly on rotary carriages of the actuator (See U.S. Pat. No. 4,430,678 to Van de Bult). These shields have been placed above the uppermost head and below the lowermost head to prevent fields produced by, for example, a motor, from interfering with data read or written by any of the protective heads.
However, it is desirable to place this servo surface on a middle disk when a large number of disks are stacked in a disk drive. Any positioning errors that might be caused by tilting of the disk stack or actuator mechanism are reduced if the servo loop uses a middle disk for sensing servo information. But, in such a configuration, a data head will be positioned above the servo head, thereby giving rise to crosstalk interference from the data head fringing field to the servo head. It is therefore desirable to avoid this crosstalk by providing a shield formed of suitable material between the data and servo heads.